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Whether it’s a cozy urban bungalow or a rambling Georgian mansion, renovating old houses is one of the best things homeowners can do for the environment. Not only are they preserving the cultural heritage and craftsmanship of a bygone era, they’re eliminating the environmental impact of constructing a new house. As preservation architect Carl Elefante of Quinn Evans Architects in Washington, D.C., puts it, “The greenest building is the one you don’t build.”But sustainable historic preservation can be tricky, as anyone knows who has tried insulating a drafty Victorian without destroying original plaster walls or leaded windows. Renovating an old house usually entails some sacrifice of the original structure to create a healthy, energy-efficient environment — but not as much as you might think.RELEARNING OLD LESSONS

Much of what we think of as modern green design was taken for granted a century ago, when most homes were built with local and recycled materials, reflective roofs, permeable walkways, operable windows, proximity to public transportation and natural-energy heating sources. “Greenbuilding is nothing new. We’re just relearning old lessons,” says Walter Sedovic, a New York architect who specializes in both historic preservation and sustainable design, and is certified by the U.S. Green Building Council’s LEED (Leadership in Energy and Environmental Design) program.

Alas, what works for building new green homes doesn’t always work for renovating historic ones. Preservationists complain that sustainable design advocates often promote new building at the expense of preservation and adaptive reuse. Even the term “sustainable building” seems to refer to new construction. “In most of the English-speaking world, historic preservation is called ‘heritage conservation,’ so there’s a direct parallel with resource and environmental conservation,” points out Mike Jackson, chief architect of the Illinois Historic Preservation Agency.

Many traditional materials and assemblies are not acknowledged by current greenbuilding standards. “Timber, for example, is considered inconsistent and prone to insect damage by today’s standards, but it’s actually far more resilient alone than with steel added [as braces and connectors], which makes it rigid,” Sedovic explains. “Buildings need to move with the seasons.”

Likewise, lime mortar and old bricks are softer, less consistent and more malleable than modern cement and bricks, qualities that have allowed old buildings to survive, Sedovic says, even through hurricanes. “There is a fallacy that stronger is better,” he says, “but with historic buildings, the ‘weakness’ of traditional materials is better suited to last for centuries.”

Going for the green in a historic home is, in many ways, the antithesis of achieving the solar-paneled modern house. Green preservation is all about invisible sustainability. “People want to say, ‘Aha! That’s the sustainable house, right there!’” says Sedovic. “But when it comes to a green historic home, what you will see is not something readily identifiable, just a traditional building doing what it was originally designed to do.”

HERITAGE ZONES

When undertaking a restoration project, it helps to divide the home into three levels of historic value, or heritage, according to Jackson. “Most important in terms of preservation is the front, the part visible to the world, and historical features just inside the front door like the fireplace, pocket doors and ceiling medallions,” he says. Original windows and exterior surfaces in this zone should be preserved if at all possible.

The sides and back of a house are considered a secondary zone, where materials like siding and windows are replaceable if necessary. The third zone is the part of the house that is invisible to the outside world, such as basements and attics, where alterations don’t affect the home’s historic appearance.

As long as it works aesthetically with the rest of the house, a kitchen can usually be updated without destroying heritage. “If you’re looking at a house built in 1900 with a kitchen from the 1970s, that history was already altered,” says Jackson. “People tend to remodel kitchens every 15 years, and the cycle is getting shorter. What you do with the kitchen is a modern question, not an authenticity question.”

Trying to make a home energy efficient is where preservation and green design objectives typically clash. But lighting and heating upgrades often can be done with minimal damage to historic features if major alterations take place in attics and basements, the least visible zone. Also, if there is sufficient space between lathe and frame, you can pump foam or cellulose insulation into the chambers behind plaster walls.

“With historic homes, the biggest issue is with windows and walls,” says Stephen Farneth, a principal at the Architectural Resources Group in San Francisco. “How do you insulate the wall assembly if the interior finishes are really outstanding? Sometimes we don’t. We find other ways of conserving energy.”

Insulating in that third zone, especially the attic and basement, should be the first step of any green restoration. Pay particular attention to the sill plate, the point where the frame meets the foundation, a notoriously leaky point in old houses. Use caulk and expanding foam where possible.

An energy audit by a utility company or energy contractor can help pinpoint trouble spots using infrared photography and/or a blower door test, in which a powerful fan device is set up in an exterior doorway to create a strong draft inside the house, making it easy to identify air leaks in the building envelope. “Owners of historic homes can cut 25 to 35 percent off their heating bills by doing an energy audit, then insulating attic and basement,” says Jim Cavallo, an energy auditor and associate editor of Home Energy magazine. Cavallo notes that he charges between $350 and $500 for an energy audit, depending on house size.

MYTHS ABOUT WINDOWS

Leaded and stained glass windows are integral to the character of an old house. Unfortunately, they are frequently as drafty as they are charming. Replacing them with vinyl or aluminum windows can drastically change the appearance of a historic house, but many people assume this is the only solution. Everyone knows double-glazed panes beat leaky, century-old singles, right?

Actually, the draft has only partly to do with glass. “At least half the problem is in the way the window meets the sash and wall structure,” says Sedovic. “Often, manufacturers’ claims of efficiency are actually a measure of the glass, not the window unit. As a result, poor choices are made relative to the expense and aggravation of doing window replacements.”

Preservationists sometimes suggest installing storm windows on the interior in order to maintain the outer appearance of original windows facing the street. However, replacement windows have pushed storm windows out of the marketplace, so you might have to look beyond your local home improvement store to find good ones.

Wooden storm windows such as the storm-and-screen combination sold by Marvin Windows and Doors are effective and authentic-looking. Less expensive options include weather-stripping and insulating wood frames with spray insulation, and reglazing panes. In general, restored wood windows look better, last longer and add more to the resale value of a historic home than vinyl or aluminum replacements.

Roofs on old houses can often be worse energy eaters than windows. “On a lot of old houses, the walls and windows are proportionally overwhelmed by the size, character and performance of the roof,” says Elefante. “In that case, don’t tear the windows out. Address the condition of the roof.”

Even a small roof can have a big impact. An experiment on a couple blocks of Philadelphia row houses a few years ago found that black tar on the flat roofs was absorbing sun and heating up the upper floors. Replacing the tar with a reflective silver coating not only reduced temperatures inside the houses but in the surrounding neighborhood as well.

A SCIENTIFIC APPROACH

Along with their aesthetic value, original materials also contain significant “embodied energy,” an environmental benefit destroyed by modern replacements. “You need to look at the fundamental quality of the materials — whether plaster walls, slate roofs, copper gutters or wood windows — and understand they have lasted a long time and will continue to last if treated reasonably well,” Sedovic says. “If a window has to be replaced in three to 10 years, how does that compare to something that’s been in place for 50 to 100? It’s important to look at the cost long-term.”

Unfortunately, there is not a lot of hard evidence to help owners of historic homes, who are contemplating “improvements” such as replacement windows, make the right decisions. “It’s hard to make a comparative discussion between the benefits of a historic casement vs. replacing it,” Sedovic admits, “because there is almost no data available.”

That may be about to change. Interest in sustainable building has led to experiments in green historic home renovation around the country. In Chicago, for example, the Historic Chicago Bungalow Association (HCBA) gathered a team of preservation and greenbuilding experts and began renovating abandoned 1920s brick homes five years ago, with the idea of sharing the results with local homeowners. Where possible, original exteriors, windows and walls are preserved and paired with various modern and efficient energy systems.

This partial insulation ended up being more cost-effective than the $10,000 geothermal system installed in a bungalow down the street.

Annette Conti, executive director of the HCBA, says she expects better results with a geothermal system the HCBA will install in a larger historic home this year. “The larger the house, the better geothermal works,” she notes. “Every project will be slightly different because every home is different and its energy use is different.”

Conti, whose background is in historic preservation, plans to focus on the issue of windows this year. “It alters an old house so much to lose the interesting old window styles,” she says. “The best compromise we’ve come up with is to save the windows on the front of the house and use [replacement] vinyl ones on the sides. Now we get to test it over the next 20 years and compare the performance of historic to vinyl windows.”

Likewise, the Green Building Program of the Office of Sustainable Development in Portland, Ore., is helping local owners of historic homes renovate responsibly. Since winters are relatively mild in Portland, insulating old houses is less of an issue than in Chicago.

Many preservationists say regional initiatives like these may be the key to preserving old homes in a sustainable way. After all, climates and conservation issues differ dramatically from one region to the next.

“What’s important in New England is very different from what’s important in Tucson, where water conservation is a big issue,” says Jackson.

One point is certain: American homes are getting older and we have to find ways to make them work effectively.

“Many people are intoxicated with the new,” says Elefante. “But step outside and look around. Everything out there has already been built. We can’t just find solutions in the cool stuff built last year. We have to find solutions to the stuff that’s already there. Tearing it all down and starting over — that’s just not a good solution.”